WEISEL, HANZEL. and NEWELL: PYGMY WHITEFISH IN MONTANA 



volume and frequency of occurrence; clado- 

 cerans were close second (Table 7). No clado- 

 cera was consumed during May and June when 

 chironomids were the main food source. Crus- 

 taceans became the prime food in July and 

 August, but in September the reliance re- 

 turned to dipterans. Cladocera apparently be- 

 came more available in October and November 

 and once more were the important source of 

 food, particularly in November. Other foods 

 were of minor importance during the months 

 when stomachs were collected. The frequent 

 presence of detritus and sand in the guts is 

 evidence that this whitefish feeds at or near 

 the bottom as visually confirmed by Heard and 

 Hartman (1966). 



Crustacea identified from the guts of pygmy 

 whitefish from Flathead Lake included an 

 ostracod; the cladocerans Daphiiia thorata, 

 D. rosea, D. longiremis, Bosima longirostiis, 

 and Leptodora ki}idtii; and the copepods Diap- 

 tomiis ashlandi, Epischiii^a nevadensis, and a 

 cyclopoid copepod. 



A December collection of spawning pygmy 

 whitefish from Ross Creek demonstrates that 

 these fish feed actively during their spawning 

 period. Fish eggs, laid by fellow spawners, 

 were the most frequently ingested food and 

 made up by far the greatest volume. Chirono- 

 mids were still taken in numbers, however, 

 along with a few other insects (Table 8). 



The feeding habits of this whitefish in other 

 lakes are usually similar to those of fish in 

 Flathead Lake. In Lake Superior, Crustacea, 

 mostly ostracods and amphipods, occurred in 

 95% of the stomachs. Chironomids were taken 

 frequently but made up only 8% of the total 



Table 8. — Percentage frequency of occurrence of food 

 items in stomachs containing food. Pygmy whitefish 

 from Ross Creek during spawning run, 12 December 

 1967. The number of fish eggs eaten ranged from 1 to 21 

 per fish with an average of 6. 



Cladocera 

 Diptera: 



Tendipedidae (chironomid larvae) 



Ceratopogonidae larvae 



Ephemeropfera: 



Heptagenia nymph 



Unknown insect remains 



Fish eggs 



Detritus and sand 



8 



38 

 3 



3 



8 



75 



33 



Empty stomachs 



9 of 50 



volume. Fish eggs, presumably coregonine, 

 occurred in collections of May and January 

 (Eschmeyer and Bailey, 1955). Pygmy white- 

 fish from a tributary of Lake Aleknagik, Alaska, 

 fed on the larvae and pupae of chironomids 

 (Rogers, 1964). In the Naknek River system the 

 relative importance of food items differs between 

 lakes. Chironomids accounted for 88% of the 

 stomach volume in some lakes but only 5% in 

 other waters. Plecopteran nymphs were impor- 

 tant as food in some lakes or outlets. Peri- 

 phyton never accounted for more than 4% of 

 stomach contents. Fish eggs, probably from 

 salmon, were taken in November (Heard and 

 Hartman, 1966). Low-rakered Alaskan forms 

 fed predominantly on bottom fauna and the 

 high-rakered fish were almost exclusively plank- 

 ton feeders (McCart, 1970). 



REPRODUCTION 



Age and Size at Maturity 



Collections of pygmy whitefish were made 

 from the inlet of Bull Lake during the spawn- 

 ing runs in December of three different years. 

 Only the last collection (1967) included a large 

 number of fish — 280, all but 4 were males. 

 The predominance of males in the three collec- 

 tions may be explained by the earlier arrival 

 of males to the spawning aggregation. None 

 of the gonads examined was spawned out. 



In the three combined collections, 50% of the 

 males were in their second growing season 

 (age I), 47% at age II, and only 3% at age III. 

 In the small sample of females, none was age I. 

 64% were age II, and 36% were age III. Except 

 for one large male with three annuli, the 

 females were consistently larger than the males 

 in each age group (Table 9). The smallest lipe 

 male was 86 mm standard length and the 

 largest was 130 mm; the smallest female was 

 120 mm and the largest was 139 mm. 



In late November and December large num- 

 bers of pygmy whitefish move from the deep 

 water of Flathead Lake and congregate at the 

 mouths of the Swan and Flathead Rivers before 

 they enter the river systems presumably to 

 spawn. The males outnumber the females 6.7:1 

 in these concentrations. Of the age I males. 



593 



